The present invention relates to substrates provided with a photocatalytic coating and the process for obtaining such a coating and its various applications. In particular, the present invention relates to coatings comprising semiconductor materials based on a metal oxide, which upon irradiation at a suitable wavelength, is capable of initiating radical reactions.
Coatings confer novel functionalities on the materials to which they are applied. These functionalities include antisoiling, fungicidal, and bactericidal properties and are optionally combined with uses such as repelling water, providing an anti-fogging layer, and optically modifying a substrate.
A wide variety of materials may be used as coating substrates. Examples of these materials are those used in vehicles or buildings, such as glazing products, walling, cladding, roofing and flooring materials such as tiles, slates, slabs and pavings. Practically any material used in the construction industry can be used as a substrate. These materials may be made of glass, metal, glass-ceramic, ceramic, cement brick, wood, stone, as well as materials reconstituted from natural materials, plastic, or fibrous materials.
Transparent substrates are typically used as glazings. These transparent substrates include glass and flexible or rigid plastic such as those made of polyester or acrylate. A particular example of an acrylate substrate is polymethyl methacrylate (PMMA).
Substrates may be classified according to their porosity. Thus, substrates may be characterized as porous, non-porous, or slightly porous. Substrates may also be regarded as a single material such as a glass substrate, or as a composite material such as a walling material which is provided with a coating of the wall-render type.
Coatings containing crystallized anatase TiO2 which have photocatalytic properties have been disclosed in patent applications WO 97/10186 and WO 97/10185. The coatings described in those references are obtained from the thermal decomposition of suitable organometallic precursors and/or from precrystallized TiO2 particles embedded in a mineral or organic binder.
The present invention is directed to substrates comprising coatings having photocatalytic properties. The coatings may additionally possess anti-soiling, bactericidal, fungicidal, anti-fogging, or water-repellant properties. They may be used also to modify the optical properties of a substrate. The coatings of the present invention comprise at least one component having photocatalytic properties and a binder which is also photocatalytic. Optional components may be incorporated into the coating. The substrates of the present invention comprise various types of materials such as glass, plastic, textile, composite materials, and walling, cladding, or roofing materials.
The present invention is also directed to a process for preparing substrates which comprises a coating as described above. Further, the present invention relates to liquid-phase dispersions used in the preparation of the coatings for the substrates of the present invention.
The coatings applied to the substrates of the present invention exhibit both a satisfactory level of photocatalytic activity and an enduring coating durability. Simultaneous optimization of the photocatalytic activity and coating durability, properties which were previously believed to be incompatible, was achieved mainly by optimizing the relative proportions of the components comprising the coatings.